Since polyurethane has excellent mechanical strength and elasticity, polyurethane has been widely used in various fields such as a coating agent, a molding material, a coating material, and an optical film, and has been also actively researched as a material for moisture-permeable waterproof cloth or synthetic leather.
However, synthetic leather coated with polyurethane was inferior in the moisture permeability, and thus there was a disadvantage of becoming musty when being worn. Therefore, as a method for solving this disadvantage, a method for wet-solidifying a polyurethane resin solution to make it porous has been proposed (for example, refer to PTL 1). However, in order to wet-solidify, it was necessary to include special equipment and a complicated processing process.
On the other hand, a hydrophilic urethane film applicable to a dry lamination method has been proposed as a method being easy in processing (for example, refer to PTL 2). However, this hydrophilic urethane film is prepared by a method of using polyoxyethylene glycol having high water absorption as a main component, and thus there is a problem in that the film swells due to water contact at the time of actual use, whereby appearance change and peeling from a base material are caused. Further, due to the high concentration of an ether group, light resistance, heat resistance, and the like are inferior, thereby providing a problem of having difficulty in expanding to furniture and vehicle applications required for durability.